The present invention relates to a spindle control system in a numerical control apparatus (CNC). More particularly, the present invention is directed to a spindle control system in which the connection between a numerical control apparatus and a spindle speed control unit is simplified.
Digitized digital spindles are now widely used for spindle motor control units in numerical control apparatuses. FIG. 2 shows a numerical control apparatus system using such a digital spindle.
In FIG. 2, numeral 1 denotes a numerical control apparatus (CNC), which reads out a machining program and delivers movement commands for various axes, a rotation command for a spindle motor, and a machine control signal for a programmable machine controller (PMC), etc., and 2 denotes the PMC which controls an actuator of a machine in accordance with commands from the numerical control apparatus (CNC) 1, and further, controls the starting and stopping of the rotation and the like of the spindle motor. Numeral 3 denotes a spindle speed control unit which has a digital arrangement and controls the speed of the spindle motor in response to a command from the numerical control apparatus (NC) 1, and further, in response to commands from the PMC 2, performs an internal sequence processing such as the rotation and stopping of the spindle motor. Numeral 4 denotes a spindle amplifier which current-amplifies commands from the spindle speed control unit 3 and controls the rotation of the spindle motor 7.
In the arrangement shown in FIG. 2, however, although the spindle speed control unit 3 itself is digitized, the interface with the numerical control apparatus (CNC) 1 is an analog signal. Further, the interface with the PMC 2 is not a bus but a discrete signal from each unit of hardware. Thus the interface of the spindle control unit 3 provides only a small amount of information and requires many cables.